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JSARIUM BLIGHT OF THE SOY BEAN 
AND THE RELATION OF VARIOUS 
FACTORS TO INFECTION 



By Richard O. Cromweu, 



A THESIS 

PRESENTED TO THE FACULTY OF 

THE GRADUATE COLLEGE IN THE UNIVERSITY OF NEBRASKA IN 

PARTIAL FULFILLMENT OF REQUIREMENTS 

FOR DEGREE OF DOCTOR OF PHILOSOPHY 

DEPARTMENT OF PLANT PATHOLOGY AND PHYSIOLOGY 



LINCOLN, NEBRASKA 
May, 1918 



Reprint from Nebraska Agricultural Experiment Station 
Research Bulletin No. 14 



FUSARIUM BLIGHT OF THE SOY BEAN 

AND THE RELATION OF VARIOUS 

FACTORS TO INFECTION 



By Richard O. Cromwell 



A THESIS 

PRESENTED TO THE FACULTY OF 

THE GRADUATE COLLEGE IN THE UNIVERSITY OF NEBRASKA IN 

PARTIAL FULFILLMENT OF REQUIREMENTS 

FOR DEGREE OF DOCTOR OF PHILOSOPHY 

DEPARTMENT OF PLANT PATHOLOGY AND PHYSIOLOGY 



LINCOLN, NEBRASKA 

May, 1918 



Reprint from Nebraska Agricultural Experiment Station 
Research Bulletin No. 14 



3 






THE OFFICIAL ROSTER OF THE STATION 

THE GOVERNING BOARD 

(the regents of the university) 
HON. EDWARD P. BROWN, President, Davey, 

Term expires January, 1921 
HON. JOHN E. MILLER, Vice-President, Lincoln 

Term expires January, 1921 

HON. PHILIP L. HALL, Lincoln Term expires January, 1923 

HON. HARRY D. LANDIS, Seward Term expires January, 1923 

HON. JOHN R. WEBSTER, Omaha Term expires January, 1925 

HON. FRANK D. JUDSON, Omaha Term expires January, 1925 

SAMUEL AVERY, Ph. D., LL. D., Chancellor 
J. S. DALES, M. Ph., Financial Secretary 

THE STATION OFFICERS 

E. A. BURNETT, D. Sc, Director 
W. H. BROKAW, Director of Extension Service 
C. A. LEWIS, B. Sc, Bulletin Editor 

THE WORKING STAFF 

L. W. Chase, M. E., A. E., Agricultural Engineering 

0. W. Sjogren, B. Sc. in A. E., Agricultural Engineering 

W. W. Burr, B. Sc, Agronomy 

T. A. Kiesselbach, Ph. D., Agronomy 

H. J. Gbamlich, B. Sc, Animal Husbandry 

L. Van Es, M. D., V. S., Animal Pathology and Hygiene 

J. H. Gain, M. D. C, Animal Pathology and Hygiene 

F. W. Upson, Ph. D., Chemistry 

J. H. Frandsen, M. S. A., Dairy Husbandry 
Lawrence Bruner, B. Sc, Entomology 
M. H. Swenk, A. M., Entomology 
R. F. Howard, A. M., Horticulture 

G. A. Loveland, A. M., LL. B., Meteorology 

E. Mead Wilcox, Ph. D., Plant Pathology and Physiology 

F. E. Mussehl, B. Sc, Poultry Husbandry 
H. C. Fillet, A. M., Rural Economics 

W. P. Snyder, M. S., Superintendent Experimental Substation, 

North Platte 
E. M. Brouse, B. Sc, Superintendent Experimental Substation, Valentine 
J. A. Holden, B. Sc, Superintendent Experimental Substation, Mitchell 
J. W. Calvin, B. Sc, Associate in Agricultural Chemistry 
W. J. Loeffel, B. Sc, Assistant in Animal Husbandry 
C K. Shedd, B. Sc. in A. E., Assistant in Agricultural Engineering 
P. L. Gaddis, A. B., B. Sc, Assistant in Agronomy 
F D. Keim, B. Sc, Assistant in Agronomy 

H. M. Martin, V. M. D., Assistant in Animal Pathology and Hygiene 
J. W. Hendrickson, A. M., Assistant in Dairy Husbandry 
John Luithly, B. Sc, Assistant in Dairy Husbandry 
C C Wiggans, Ph. D., Assistant in Horticulture 
H. 0. Werner, B. Sc., Assistant in Horticulture 
J O. Rankin, A. M., Assistant in Rural Economics 



CONTENTS 

Introduction 5 

Economic Importance of the Soy Bean 6 

Other Soy Bean Diseases 7 

History, Occurrence and Importance of the Disease 8 

Symptoms' 10 

Etiology 13 

Comparison of the Soy Bean Species of Fusarium with Other Wilt-Pro- 
ducing Species of the Genus 16 

A. Source of Cultures and Methods of Isolation 16 

B. Culture Media and Their Various Effects on Species of 
Fusarium 18 

C. Methods of Study and Presentation 19 

D. Results of the Comparison of the Soy Bean Fungus With other 
Members of the Section Elegans 20 

Morphological and Cultural Comparison of the Fusarium Species on Soy 

Bean with F. Tracheiphilum 23 

Inoculation Experiments 25 

Experiments on the Relation of Various Soil Factors to Infection of 
Soy Beans by F. Tracheiphilum 30 

A. The Influence of Soil Types 30 

B. The Influence of Acidity and Alkalinity 33 

C. The Influence of the Nematode (Heterodera Radicicola) ..35 

D. The Influence of Soil Temperature 37 

E. The Influence of Other Organisms 38 

Field Experiments to Determine the Susceptibility of Varieties 38 

Summary 41 

Literature Cited 42 



FUSARIUM BLIGHT OF THE SOY BEAN AND 

THE RELATION OF VARIOUS FACTORS 

TO INFECTION 

BY RICHARD O. CROMWELL 

Extension Plant Pathologist, 
Iowa State College 1 

During the summer of 1915 and each succeeding summer, 
packages of diseased plants of the soy bean Soja max (L.) Piper 
(20) 2 - 3 were received at the North Carolina Experiment Station 
from several correspondents. A large number of plants in the fields 
from which these specimens were taken had become stunted or 
chlorotic, or were dead. The plants received were still green and 
in good condition for examination. The evidence obtained from 
a preliminary inspection indicated that the diseased condition 
was due to the presence of a fungus belonging to the genus 
Fusarium. Furthermore nearly all of the isolations from this 
material gave apparently pure cultures of a species of Fusarium. 

Because of the importance of legumes in the cropping systems 
of the Piedmont and Coastal Plains sections, and because of the 
seriousness and extent of Fusarium diseases of members of this 
and thirteen other plant families, 4 an investigation was outlined 
(1) to determine the parasitism of this species of Fusarium on 
soy bean, (2) to establish its relationship to Fusaria of the section 
Elegans in so far as a comparison of the cultural characters per- 
mitted, and (3) by means of cross inoculations and field studies 
to determine the relationship of this disease of soy beans to the 
wilt disease of cowpeas (Vigna sinensis Hassk.) caused by 
Fusarium tracheiphilum Smith. 

The results of these investigations up to the close of the sum- 
mer of 1016 have been reported by the writer (6). The studies 
were conti nued at the North Carolina Experiment Station until 

formerly assistant plant pathologist, North Carolina Experiment Station The 
writer is indebted to the North Carolina Experiment Station for leave of absence in 
order that full time could be given to these studies. Submitted for publication June, 1918. 

2 Reference is made by number to "Literature Cited," pp. 

8pipe n, ^ 20 - ) gives the following as the full synonomy of the soy bean: 

Phaseolus max L. 

Dolichos soja L. 

Soja hispida Moench 

So] a japonic a Savi 

Glycine soja Siebald and Zuccarini 

Soja angustifolia Miguel 

Glycine ussuriensis Regel and Maack 

Soja max (L.) Piper 
•Wollenweber (31, p. 35) 



G Agricultural Experiment Station Research Bulletin 14 

the fall of 1917 and then at the University of Nebraska. A re- 
vised report of them is given in this paper. Additional studies of 
the soy bean blight, the results of which are also reported here, 
were planned to determine the effect of various factors on the 
amount and severity of the disease. 

The writer wishes to express herein his sincere thanks to 
Doctors F. A. Wolf and E. M. Wilcox for their assistance and 
criticism during the time these studies were being conducted in 
connection with their departments. 

ECONOMIC IMPORTANCE OF THE SOY BEAN 

The soy bean is a native of tropical Africa, Asia, and Australia 
(26, p. 360-361; 20,43. 76) and was introduced into Europe by 
Kampfer about 1690 (21, p. 9). At the present time it is the 
most important legume grown in Japan, China, and Manchuria. 
The soy bean is the chief source of protein in human food in 
Japan, where very little meat, except fish, is eaten as compared 
with the amount of meat consumed in this country. Its culture 
in England was begun in 1790. The plant was introduced into 
the United States from Japan in 1860. Since that time its culti- 
vation as a soil-improving and a forage crop has been confined 
for the most part to the Southern States. North Carolina is 
probablv foremost among these States in the production of soy 
beans. The yield in 1909 was only 13.313 bushels (29, p. 632). 
and in 1915 was estimated 1 as approximately 1,000,000 bushels. 
Within the last three or four years, and especially since the war 
began, this crop has become increasingly important because of 
the large variety of products manufactured from the oil and meal 
and because of its introduction in the United States as a human 
food. 

The following is a list of the most important products 
obtained from soy beans or in which soy beans enter : Soy bean 
milk, vegetable cheese, meal or flour, macaroni preparation, soups, 
pork and beans, meat substitutes, toilet powder, fertilizer, and 
cattle feed from the meal, and high explosives, soaps, linoleum, 
rubber substitutes, margarine, Japanese sauce, paints, varnishes, 
water-proof cloth, salad oil, lubricants, and lard substitutes from 
the oil. 

The grain is more valuable as a supplementary feed than 
cottonseed meal for the production of pork, mutton, beef, wool, 
milk, and butter. The seed contains 34 per cent protein and 
47 per cent fat. A bushel contains more than three times the 
amount of digestible protein, fat, and ash that is contained in a 

1 Estimate furnished by the North Carolina Experiment Station. 



Fusarium Blight of the Soy Bean 7 

bushel of corn. Soy bean hay contains 2.48 per cent nitrogen, 
0.40 per cent phosphoric acid, and 1.32 per cent potash. 

It has been found in most of the soy bean growing sections of 
the South that an acre will produce on the average something- 
like two-thirds to three-fourths as many bushels of soy beans as 
of corn and the price brought by soy beans has always been 
from 50 to 100 per cent greater. 

During 1915, $9,000,000 worth of oil alone was imported. 
Cottonseed oil mill owners have been induced, however, partially 
by the efforts of members of the staff of the North Carolina Ex- 
periment Station, to crush soy beans during their otherwise idle 
season. The few mills in the State which have clone this have 
found a ready market for the oil and meal. 

OTHER SOY BEAN DISEASES 

Soy beans are very generally observed to be quite free from 
disease, and no very seriously destructive parasites of this host 
appear to have been reported in the literature at hand. Of those 
reported, a detailed study has not been made, except in the case 
of Bacillus lathyri Manns and Taubenhaus (16, IT). The accounts 
of the other diseases consist of brief fragmentary mycological 
notes and mention of their place of collection or of their appear- 
ance. Since any of them may appear on plants affected with 
blight or wilt, it is deemed advisable to call attention to the pub- 
lished accounts of these diseases and the appropriate bibliography. 

Septoria sojina v. Thumen (on living or declining leaves) (27). 

Pliyllostica sojaecola Massalongo (18, p. 688). 

Aecidium glycines P. Henn. (8, p. 52). 

Uromyces sojae (P. Henn.) Sydow (25, p. 429). 

Bacillus sp. (on leaves)— Heald (11, 12), Smith (24), and Clinton (4). 

Bacillus lathyri Manns and Taubenhaus (on leaves and pods) (17), 

and Manns (16). 
Heterodera radiciola—Scofieia (22, p. 9), Gilbert (10, p. 9), Bessey 

and Byars (2, p. 8). (These authors merely mention the soy bean 

as a host for this parasite.) 
Chlorosis and crinkling (cause?). (Description of the disease in the 

field.) Clinton (5). 
Septoria glycines T. Hemmi (comparison with S. sojina above) (13). 

A disease due to Sclerotium rolfsii is the only one not re- 
ported which the writer has observed to seriously injure the crop. 

It is not believed that the presence of any of these organisms 
would lead to confusion in the diagnosis of blight caused by the 
species of Fusarium under consideration. 



8 Agricultural Experiment Station Research Bulletin 14 

HISTORY, OCCURRENCE AND IMPORTANCE OF THE DISEASE 

No published report of a disease of soy beans caused by any 
species of Fusarium and one account only of attempts to produce 
a disease of this host with the cowpea wilt organ ism have been 
brought to the writer's attention. Orton (19, p. 16-19) conducted 
these tests at Edisto Island, S. C, in 1900, and at Monetta, S. C. 
He says (p. 18) : 

"Eight varieties (soy beans) were tried on ten plats. All 
proved to be immune to the wilt disease, but none of them was 
adapted to the local conditions. The growth was very small, the 
plants averaging from 8 to 14 inches high, tho most of the 
varieties bore a good crop of seed for such small plants. All 
suffered from much drought in midsummer and all were badly 
injured by the root nematode. On examination of the roots a 
moderate number of bacterial tubercles were found. * * * 
They (soy beans) were at a considerable disadvantage in this test 
on account of the late date of planting and the ensuing dry 
weather." 

The varieties tested were Tokio, Buckshot, Yosho, Ito San, 
Manhattan, Guelph, and Amherst. 1 Orton reported that at 
Edisto Island the soy bean made a heavy growth, 3 or 4 feet high, 
and was free from the wilt disease. It may be said that a very 
considerable proportion of the several varieties of cowpeas grown 
in adjacent plots succumbed to wilt. The results of these tests 
accord with the observations of others who have had opportunity 
to observe these crops when they were grown on soil known to be 
infested with cowpea wilt. 

A limited number of careful observations have therefore been 
made during 1915 and 1916 to determine whether the Fusarium 
diseases of these two hosts are coextensive in range and thus to 
furnish evidence of the identity of the two. Two 5-acre fields on 
widely separated parts of the North Carolina Experiment Station 
farm, in which cowpeas and soy beans were grown in alternate 
rows, showed a very considerable proportion of the former host 
affected, whereas the latter remained entirely free from disease. 
In other localities of the State, soy beans growing on soil infested 
with the cowpea-wilt organism have remained disease-free. 

Observations differing from these were made in the case of 
soil brought from another part of the Station farm. When this 
soil was used to grow soy beans in pots out of doors, it was found 
to be infested with the soy bean-blight organism, as shown by the 
development of the disease in 33 of the 80 jars (Plate 95, D and 



1 The names in use for these varieties in 1890 were respectively as follows: Best 
Green, Early Black, Yoshoka, Rokugatsha, Gosha, Black Round, Green Medium, and 
Bakaziro. 



Fusd riu m Blight of the Soy Beau 



9 



E). Wilt of cowpeas and blight of soy beans were present on the 
farm of one of the correspondents previously referred to, at Red 
Springs, N. C. Many of the soy bean plants in this field were 
killed and many only stunted, so that a decrease in yield of 60 per 
cent during the season of 1918 is probably a correct approxima- 
tion of his loss. Blight of soy beans has also been found to occur 
at Exum and Belhaven, N. G, and was the cause of considerable 
loss in both locations. The first of these soils occurs in the eastern 
(h\<x^ of the Piedmont and the others in the Coastal Plains section 
of the State. 

Dr. W. H. Tisdale, in conversation with the writer in 1917, 
said that while at Madison, Wisconsin, his attention was called 
to diseased soy beans growing in experimental plots which seemed 
to be infected with a species of Fusarium. Upon being shown 
specimens of the soy bean blight, he stated that the diseased 
plants looked very similar to those he had previously seen. 
Dr. Gr. L. Peltier wrote from the Alabama Experiment Station in 
the fall of 1917: ""It (soy bean blight) was quite common here 
on the station farm, and I isolated a Fusarium from the infected 
material." 

Cowpea-wilt has been found in many localities in parts of 
the United States. It is also entirely probable, if we judge from 
the results to be presented subsequently, that the soy bean-blight 
may appear more or less generally wherever the soil is infested 
with Fusarium iracheiphilum. Records received from the office of 




Fig. 1 — The ruled area indicates the states that have reported the presence of 
Fitsui turn trackeipHiiutn. 



10 Agricultural Experiment Station Research Bulletin 14 

Plant Disease Survey show that, up to January 1, 1918, F. 
tracheiphilum has been reported as being productive of losses to 
cowpeas ranging from 2 to 100 per cent in Indiana, Missouri, 
Mississippi, Louisiana, Texas, Oklahoma, Georgia, Florida, North 
Carolina, South Carolina, Virginia, Arkansas, and Tennessee. 
These states are blackened in the accompanying map (fig. 1). 

SYMPTOMS 

In 1916, soy beans were planted during the last two weeks in 
May. This is somewhat later than usual, being due to the late 
season and a period of drought. When the plants were 4 weeks 
old, they had attained a height of 2 to 3 dm. and were apparently 
still free from disease. The disease was first observed on July 25, 
when the affected plants were about 8 weeks old. Symptoms of 
the trouble could probably have been found a week or two earlier. 
Affected plants, all of the same age but varying in height from 
2 dm. to 1 meter, were observed on the 25th. The fungus is 
believed to have stunted these small plants. In no case has the 
disease been observed to occur on seedlings under field conditions. 
In sand inoculated with pure cultures, however, a number of 
seedlings became diseased as described later in this paper. 

In 1917, soy beans were planted in the same field on April 26. 
The weather was cool with considerable rain for the following 
week or ten days so that on May 27 the majority of the plants 
had only just broken thru the surface of the soil, some were not 
yet up, and some were from 10 to 12 cm. in height. Examination 
of a few of the plants from a number of the rows did not show 
injury that could be attributed to Fusarium. On June 12 some 
of them were 15 to 25 cm. in height and infected plants were 
found in many of the rows. On June 26 the plants were 8 weeks 
old and from* 3 to 5 dm. in height. Many were stunted by this 
time, partly because of the action of Fusarium and partly because 
of nematodes, fihizoctonia, and other causes, so that only by 
removing suspected plants could it be certain that they were 
diseased and that Fusarium was quite generally present thruout 
the field. Plants were found without any of the external symp- 
toms described below, except the dwarfing, the xylem areas of 
which were browned well up the stem. By July 20 the disease 
was present thruout the field and many plants were in advanced 
stages of the disease. 

Comparing the conditions in 1917 with those of 1916 in the 
same field, one^ finds that at the end of 8 weeks the plants were 
smaller in 1917 but the disease was more general and more ad- 
vanced in its injury to the individuals. 



Fusarium Blight of the Soy Bean 



11 



m appearance of five healthy and five diseased 
Figure 3, D. E. The same type of sandy loam 



The contrast in 
plants is shown in Figure i>, JL>. Jii. The same typ 
soil was used in both jars and the plants in each were grown out 
of doors under the same conditions. The plants shown in figure 
E were naturally infected from naturally infested soil and were 
typical of the diseased plants in 32 other jars of the 80 in the 
test. A considerable number of the leaves have fallen from the 
diseased plants, a portion of the petioles persist without leaflets, 
the plants are dwarfed, and there is no evidence of wilting in 
any part of the plants. The foliage which persists on these plants 
is yellow ;is contrasted with the normal leaf green of healthy 
plants. 




Fig; -' — A. A diseased stem of soy bean, showing the roughened appearance caused 
by the irregular covering of sporodochia. 

B. Interior of healthy (unstained) stem of soy bean. 

C. Interior o( diseased (discolored) stem of soy bean. 

The occasional absence of a definite wilting of the leaves 
has been noted in other wilt diseases. Orton (19, p. 10), in speak- 
ing of the cowpea disease caused by F. tracheiphilum, says : "The 
term 'wilt' is somewhat misleading, as the leaves usually drop off 
before there is any conspicuous wilting. The name was applied 



[•2 Agricultural Experiment station Research Bulletin 14 

because of its relationship to the wilt of cotton and watermelon, 
where this symptom is very prominent, and it seemed desirable to 
retain it for the cowpea disease." 

In the case of the soy bean disease, wilting is a less prominent 
symptom than in cowpeas, and is seldom present at any stage of 
the disease. The plants, as a rule, drop all of their leaves and die 
without any evidence of wilting. Wilting has been observed 
in a very few instances in the field in the case of young plants. 
The woody nature of the stem and petioles probably accounts 
for the general absence of wilting in them, and the presence of 
well-developed mechanical tissues in the leaflets may account for 
their failure to manifest wilt. The possibility exists, also, that the 
physiological interaction of parasite and host differs from that 
exhibited by wilted cotton and watermelons infected with 
Fusarium spp. If potted soy beans which have never been ex- 
cessively watered are allowed to remain without water they do 
not wilt but the leaves finally curl as the tissue becomes dry and 
crisp. Neither do the leaves wilt if the stem is cut to the center. 




Fig. 3 — D. Soy bean plants grown out of doors in the same type (Cecil) sandy loam 
soil; D, healthy; E, diseased thru the naturally infested soil. 



Fusarium Blight of the Soy Bean 13 

Instead of applying the name "wilt," therefore, to the soy 
bean trouble, it is thought desirable to call it "blight," This 
word describes the most prominent symptom on the foliage, 

That plants are often almost indifferent, for some time, to the 
fungus which may even be abundantly present within it, is shown 
not only by the absence of wilt but also by the fact that many of 
the plants mature a reduced crop of beans in spite of the disease. 
Affected plants in such cases are stunted and mature earlier than 
healthy plants. In contrast to this, 100 per cent of the cowpeas 
in rows in different parts of the same field are infected, most of 
them die before reaching a height of 2 dm., and the scattered 
plants then remaining may all die before blooming. 

Perhaps the most prominent symptom is a browning of the 
interior of the stems and roots. By the time the lower leaflets 
or leaves begin to drop, this discoloration is evident well up into 
the stem and, if necessary, by removing the petioles, infected 
plants may be noted from the brown color of the bundle scars 
when no other positive symptom is to be observed. As the dis- 
ease progresses, the discoloration extends in some cases to the tip 
of the stem and into the bundles of the leaflets. The tracheal 
tubes of affected stems when cut obliquely show as brown specks. 
The relative amount of discoloration in general and the depth 
of color in affected xylem portions is less in soy beans than in 
cowpeas. Healthy and diseased stems are shown in Figure 2, B 
and C, respectively. 

The surface of stems of plants in advanced stages of the dis- 
ease in the field generally have salmon-colored spore masses, 
sporodochia, thickly and irregularly distributed over them. 1 This 
character is shown by the roughened appearance of the stem in 
Figure 2, A. The spore masses are composed of macroconidia of 
the fungus and are frequently found to occur on plants, the upper 
leaves of which are still healthy in appearance. Sometimes they 
are formed only in more advanced stages of the disease. 

ETIOLOGY 

Sterile seedlings had been grown in test tubes by the method 
described later in this paper for use as a culture medium to main- 
tain the virulence of the organism. In 1915 the roots of such 
seedlings, inoculated after the development of the first true leaves, 
were found in a few days to be penetrated by the fungus thru 
stomata and epidermis. The roots were mounted directly on slides 
in a o-lvcerin-eosin water solution and examined under the micro- 



1 Sporodochia on stems of cowpeas are reported by Orton (19, p. 9) to appear after 
the death of the plants. 



14 Agricultural Experiment Station Research Bulletin 14- 

scope. Tisdale describes practically the same method in a recent 
paper (28, p. 576). Under such unfavorable conditions, however, 
the host was at a disadvantage, and since a number of other 
species of Fusarium penetrated the plants in the same way, no 
significance is given to the observations. 

In order to determine the relation of the organism within the 
various host tissues, a large number of stained free-hand and 
microtome sections were made of stems and roots at various stages 
of development of the disease. A number of attempts to obtain 
pieces of roots at the time of infection were, however, unsuccess- 
ful. In woody stems, in an early stage of the disease, only the 
xylem tubes nearest the pith were found to contain the fungus 
filaments. The pith had disappeared in both normal and diseased 
plants of moderate size. Later, other of the tubes thruout the 
xylem area were penetrated and had become filled to a large extent 
with a network of fungous filaments. In still more advanced 
stages, all of the xylem elements (fig. 4, H) were found to contain 
the fungus, and in addition the cortical parenchyma was invaded. 
Many of the fibrous roots were destroyed, and figure 5 shows 
how the disease progresses from the smaller root branches into 
the main root. A and C represent the cortex and pith, respec- 
tively, and are, at this stage of the disease, seen to be free from 
discoloration due to the fungus. B indicates the xylem region, 
which is discolored in areas beginning at the point of origin of 
lateral roots and extending mostly upwards. Later the browned 
areas become continuous and the xylem is found to be in this con- 
dition thruout the stem and root (fig. 2, C). New roots form, 
but often of insufficient number to maintain the life of the plant. 
In other cases the plants subsist with a reduced supply- 
It seems, therefore, that the symptoms produced result not 
simply from (1) a mechanical clogging or (2) a slow appropria- 
tion of food and water by the fungus, as others have previously 
stated, but that (3) a considerable destruction of the root system, 
and, perhaps, (4) a reduction of the activity of the protoplasm 
due to the possible presence of toxins secreted by the fungus, also 
aid in this. 

That other organisms may often facilitate the entrance of 
Fusarium is given special consideration in another part of this 
paper. 



Fusarium Blight of the Soy Bean 



15 




Fig. 4 — A-u, Types of macroconidia of the species of Fusarium on soy bean. H, 
Cross section of the xylem portion of a diseased soy bean stem, showing the invasion of 
the medullary rays (a) and the xylem vessels (b) by mycelia of the species of Fusarium 
on soy bean. 



16 Agricultural Experiment Station Research Bulletin 14 




Fig 5 — Diagrammatic drawing of a longisection of the main 
root of the soy bean to show the entrance of the fungus from 
the lateral roots. A and C indicate uninvaded pith and cortex, 
respectively. B represents the discolored xylem in an early 
stage of the disease. 



COMPARISON OF THE SOY BEAN SPECIES OF FUSARIUM WITH 
OTHER WILT-PRODUCING SPECIES OF THE GENUS 

SOURCE OF CULTURES AND METHODS OF ISOLATION 

Isolations were made from the interior of stems of freshly 
wilted soy bean and cowpea plants. The stems were first thoroly 
washed in water and allowed to remain wrapped in cotton mois- 
tened with 0.1 per cent solution of mercuric chlorid for 15 
minutes. They were then split open so that the diseased interior 
was exposed. Fragments of diseased tissue were removed with 



Fusarium Blight of the Soy Bean 17 

a sterile scalpel and transferred to cooled poured plates of string- 
bean agar (8 c.c. per plate), to each of which four drops of 20 
per cent lactic acid had been added. After several days, a micro- 
scopic examination was made of the conidia and mycelium to 
determine whether other organisms were present. Eight trans- 
fers to test-tub- slants were made from the margin of several 
plantings and kept for comparison and for indications of con- 
tamination. It may be noted that a large percentage of pure 
cultures was obtained by this method. From the cultures that 
were pure, single-spore cultures were obtained according to the 
method described by Sherbakoff (23, pp. 102-103; p. 101, footnote 
8). Stock cultures were made from these single-spore cultures and 
repeatedly repoured to protect from subsequent contamination. 

Several species of Fusarium were secured, in order to com- 
pare them with the Fusarium sp. from the soy bean and the one 
from the cow pea. isolated as described above. The following- 
si >ecies, subcultures from Wollenwebers authentic cultures, were 
obtained thru the courtesy of Mr. C. W. Carpenter, of the Bureau 
of Plant Industry : Fusarium oxysporum (Schlecht.), F. vasin- 
fectum (Atk.), F. lycopersici Sacc, F. niveum Smith (members 
of the section ElegansJ, and F. discolor, var. sulphureum 
(Schlecht.) App. and Wollenw. (1, pp. 115-118), (section 
Discolor). 

These species were studied in culture, in order to determine 
their morphological and cultural character,-;, since such a study 
is considered of primary importance in their differentiation. The 
species mentioned were chosen because all except one belong to the 
section Elegans, the section which contains the known wilt-pro- 
ducing species, and because, according to Wollenweber, they are 
the most difficult to separate by this method. F. congluimans 
Wollenw., F. redolens Wollenw., and F. orthoceras App. and 
Wollenw., of the same section are included in the comparisons. 
They are so different from the others, as indicated by the original 
descriptions, that the writer soon realized that there was little 
probability of confusing them with the soy bean strain. Wollen- 
weber (31. 32) and Sherbakoff (23) have described other species 
and varieties of the section Elegans, which are not, however, in- 
cluded iu this study, because they occur on hosts widely separated 
genetically from the soy bean 1 and because the authors have not 
had opportunity to make a sufficient number of infection experi- 
ments to establish them as wilt producers. 



1 Wollenweber, H. W. (31, p. 37) says, "The parasite from one host has not been 
found on living organs of another host. In pure culture the parasite from one host 
did not cause wilt in any other host as a result of inoculation experiments." 



18 Agricultural Experiment Station Research Bulletin 1^ 

CULTURE MEDIA AND THEIR VARIOUS EFFECTS ON SPECIES OF 

FUSARIUM 

In making a cultural study of these fungi much care was 
taken to follow the suggestions of Appel and Wollenweber (i), 
Wollenweber (31, 32), and Sherbakoff (23), in order to determine 
what criteria to employ in judging normal growth characters. It 
is generally believed that standardization of cultural methods is 
highly essential in the comparative study of so difficult a group 
of fungi. 

The writer has kept the soy bean and the cowpea strains 
under constant observation for three years and other strains for a 
part of this time, on various kinds of "natural and artificial 
media" and under widely variable physical conditions. He is 
therefore familiar with the possible variability of members of this 
genus. 

Since a large number of the media used did not prove to be 
of. special diagnostic value, they are not discussed here. Among 
the media most commonly employed and serving some particular 
purpose were oat, potato, and string-bean hard agars (3 per cent 
agar), which, because of the paucity of moisture (23, p. 106), 
give all forms of fructification with "normal" spores. Five to 10 
per cent of dextrose was added to agars to favor the production 
of pigment. The addition of this sugar, however, favored the 
development of mycelium at the expense of macroconidia, and 
when from 8 to 10 per cent was added these spores were often 
absent. Growth on steamed rice in test tubes from weighed 
quantities of rice and measured amounts of water to obtain uni- 
formity also results in the formation of pigment and sometimes 
an odor that is typical for certain related species of Fusarium. 
Herbaceous and woody stems, string-bean pods, and potato plugs 
give the best development of sporodochia and pionnotes. 1 Potato 
plugs also serve for the proper development of sclerotia and 
colors, both of which may be reduced or absent from stem plugs 
when there is a minimum development of mycelium. 

According to Wollenweber (31, p. 37), virulence is commonly 
maintained on stem plugs. Living sterile soy bean and cowpea 
seedlings grown in 6-inch test tubes were also used and are 
thought to be a better medium for maintaining virulence in the 
strains from the respective hosts. 

In order to obtain sterile seedlings for this purpose the seeds 
were first washed for 5 minutes in tepid water and were then 
placed in concentrated sulphuric acid for 20 minutes. Formalin, 
mercuric chlorid, both in aqueous and alcoholic solution, and 



1 For a discussion of these terms, see Wollenweber (31, p. 24). 



Fusarium Blight of the Soy Bean 19 

other disinfectants were employed with much less success. After 
washing off the acid in three or four changes of sterile water, the 
seeds were transferred into sterilized moist chambers in the bot- 
toms of which several layers of moist filter paper had been placed. 
Germinated seeds on which there was no evidence of contamina- 
tion after a day or two were transferred to sterile test tubes 1 the 
bottom of each of which contained a wad of moistened filter 
paper. 2 If, during germination or transfer, contamination occurs, 
it generally becomes evident on the seedlings or white paper, 
especially if the seedlings are set aside until they have grown to 
a height of 3 or 4 inches. 3 

More recently, however, such precaution to maintain virulence 
was found to be unnecessary because the age of cultures seemed 
to have little effect upon their virulence. Old cultures gave as 
high a percentage of infection, if grown on proper media and 
transferred frequently, as they did when first isolated. 

METHODS OF STUDY AND PRESENTATION 

All transfers of different strains in a set for comparison were 
made to a certain medium on the same day and to additional 
media to provide the necessary cultural characters. When species 
were compared, they were always of the same age and were grown 
on the same medium. As many comparisons could be made on 
the same day as there were species and kinds of media in the set. 
If sufficient data had not been obtained, if certain cultures were 
abnormal, or if other species or media were to be used, new sets 
were prepared of all of the species using the desired media and 
comparisons were again made thruout the series. 

Cultural differences also arise as a result of the employment 
of spores or a bit of mycelium in inoculation. In the former case 
the young cultures quickly produce spores with a scant mycelial 
growth, while in the latter the mycelial growth is abundant and 
there is a paucity of spores. For this reason spores from sporo- 
dochia, when present, were used, and in all cases, in so far as was 
possible, the same kind of inoculum was transferred for all cul- 
tures of a set. When the production of spores becomes subnormal, 
as it often does in cultures, considerable time and patience may be 
required to bring the strain back to a "Xormkultur." This was 

1 For making this last transfer, dip the ends of long tweezers into 95 per cent alcohol 
and ignite in the flame. This sterilizes instruments, burns off the excess of alcohol, 
and leaves them dry and cool enough for immediate use. 

2 The use of agar as a substratum for this purpose (Garman and Didlake, 9), and 
Sphagnum moss, did not prove to be satisfactory. Soil, too, has a disadvantage in that 
it does not show the contaminations as readily as filter paper or agar. 

3 An oat sprouter with glass front, heated by a kerosene lamp and costing about 
$10, makes a good light incubator for such purposes when the greenhouse is not con- 
veniently located or the temperature suitable. This sprouter is unsuited, of course, to 
cultures or material requiring a constant temperature. 



20 Agricultural Experiment Station Research Bulletin 1^ 

accomplished by transferring a small portion of mycelium to a 
variety of media until a medium was found on which spores 
were again obtained. 

All cultures were kept in the laboratory at room temperature, 
12° to 26° C, and in diffused daylight, so that they were sub- 
jected alike to any change of environmental conditions. 

In all cases 10 cultures of a species were made on each 
medium. Different forms of fructification which normally appear 
on a certain medium may not do so in every tube. For example, 
in a species in which sporodochia are not abundant, they may 
perhaps form on only 2 or 3 of the 10 stem plugs; or if the form 
produces green sclerotia, they may develop on not more than 5 of 
the 10 potato plugs. In some instances as many as 8 to 10 sets of 
10 tubes each of a particular species were made. 

In making the microscopical examination, note was taken of 
the size, septation, abundance, and type of conidia (fig. 1, A-G), 
chlamydospores, and conidiophores. In measuring spores, several 
fields were first examined to fix in mind the prevailing type and 
an average of 10 or more of these typical spores was made. Care- 
ful note was taken also of extreme types. 

In the macroscopic study of the cultures, the nature of the 
stromata, the pionnotes and sporodochia, the character of the 
aerial mycelium, the color of spore masses, aerial and submerged 
mycelium, and substratum, and the production of sclerotia were 
considered. 

RESULTS OF THE COMPARISON OF THE SOY BEAN FUNGUS WITH 
OTHER MEMBERS OF THE SECTION ELEGANS 

The first sets of parallel cultures were intended to serve in 
the separation of any or all of the species of Fusarkim causing 
wilt from the soy bean fungus. F. discolor, var. sulphureum, 
F. oosysporum, F. vasinfectum, F. h/copersici, F . niveum, F. tra- 
cheiphilum, and Fusarium sp. from soy bean were therefore 
crown on the followine; media, several sets of 10 cultures of each 
species being used on each medium: Potato plugs, steamed rice, 
cotton steins, potato hard agar, and string-bean hard agar. The 
cultures were examined when 8, 15, 19, 30, and 50 days old. The 
results are noted in Table 1. Only those characters are recorded 
that are necessary for the separation of the species. 



Fusarium Blight of the Soy Bean 



21 



Table 1. — Characters which separate a number of the wilt-pro- 
ducing species of Fusarium from F. tracheiphilum and 

the soy bean fungus. 



Species 
F 


Sclerotia 


Sporodochia 


Pionnotes 


Chlamydospores 


. discolor 


None 


Numerous 


Perfect 


Intercalary; no 
measurements. 


F. vasinfectum .... 


Green and 
flesh-colored 


do 


do 


Intercalary and 
terminal; no 
measurements. 


F. oxysporum 


do 


Few 


Reduced 


Intercalary and 
terminal; 6 to 
12 n- 


F. lycopersici 


Flesh-colored 


Numerous 


Perfect 


Intercalary and 
terminal; no 
measurements. 


F. niveum 


Large green 


do 


Reduced 


Same as for F. 
lycopersici. 


F. tracheiphilum. . . 


Green and 
flesh-colored 


Few 


None 


Intercalary and 
terminal; 6 to 
12 ix. 


Fusarium sp. on 
soy bean 


Mostly green; 
some flesh- 
colored 


do 


do 


Same as for F. 
tracheiphilum. 



22 Agricultural Experiment Station Research Bulletin 14 



Table 1 (Continued). — Characters which separate a number of 

the wilt-producing species of Fusarium from F. tra- 

cheiphilum and the soy bean fungus. 



Species 


Macrcconidia 


Odor 


Size of 3-septate 


Type 


F. discolor 


No data 


Discolor; mostly 

5-septate 


None. 




Same as in F. 
oxysporum 


Elegans; mostly 

3-septate 


Strong lilac on rice. 


F. oxysporum 


28.7 to 35.6 by 
3.6 to 4.1 M 


do 


Often none, some- 
times scant lilac. 


F. lycopersici 


Abnormal 


do 


None. 


F. niveurn 


Abnormal; (orig- 
inal description 
gives larger than 
F. oxysporum). 


do 


do 


F. tracheiphilum. . . 


23.6 to 41.0 by 
3.9 to 4.1 n 


do 


do 


Fusarium sp. on 
soy bean 


24.6 to 35.8 by 
2.89 to 4.1 /x 


do 


do 



From the data in Table 1 it is important to observe that 
F. tracheiphilum and the species of Fusarium on soy bean belong 
to the section Elegans, as established by Appel and Wollenweber 
(1) and modified by Wollenweber (31) in a subsequent study. 
They are themselves very similar in cultural characters, but can 
be quite sharply separated from the other species included in the 
tabulation. When the characters of the species of Fusarium on 
the cowpea and soy bean noted in this table are compared with 
those in the original descriptions of certain other members of the 
section Elegans — namely, F. redolens, F. orthoceras, and F. con- 
glutinans — there is plainly no chance of their confusion. F. 
redolens (31) produces no blue sclerotia, and its conidial masses 
are brownish white; F. orthoceras (25) possesses neither sclerotia, 
sporodochia, nor pionnotes; and F. conglutinans (31) is distin- 
guished because of the absence of sclerotia, sporodochia, or pion- 
notes, and the typical wine-red to purple colors of the section. 



Fusarium Blight of the Soy Bean 



23 



MORPHOLOGICAL AND CULTURAL COMPARISON OF THE 
FUSARIUM SP. ON SOY BEAN WITH F. TRACHEIPHILUM 

Since the studies summarized in Table 1 do not succeed in 
distinguishing the species of Fusarium on soy bean and cowpea, 
a more extensive cultural study of these two fungi was made. 
For this purpose three series of cultures were grown, and the 
results have been summarized in Table 2. Each series contained 
10 cultures of each fungus on stem plugs, potato plugs, steamed 
rice, standard nutrient agar (1.8 per cent agar, 1.0 per cent acid), 
string-bean hard glucose agar (3 per cent agar, 1.0 per cent acid, 
and 10 per cent glucose), and oat hard agar (3 per cent agar and 
1.0 per cent acid). The cultures were examined when they were 
8, 15, 30, 50, and 75 days old. 



Table 2. — A morphological comparison of the 
Fusarium on soy bean and coiopea. 
Fusarium sp. on soy bean. 



species of 



Medium 


Macro- 
conidia 


1 
Sporodochia j Sclerotia 


Color of 
mycelium 


Character 
of mycelium 


Standard 
nutrient 
agar 


No measure- 
ments 


Salmon- 
colored 


None 


White 


Mostly aerial 
and floccose, 
becoming ap- 
pressed in 
old age. 


String-bean 
agar 


do 


Salmon- 
colored; 
generally 
present 


Green 


do 


do 


Oat, hard 
glucose 
agar 


26.6 to 38.6 
by 3.69 to 
4.92 fx, 50 
days old 


Flesh- 
colored 


Dark-green 


Mostly lilac; 
some dark 
purple 


Cottony. 


Steamed rice 








Reds, pinks, 
lilacs, 
purples 














Potato plugs 


Normal 
spores 
absent 


Salmon- 
colored; 
generally 
present on 
sclerotia 


Dark-green 


Green, near 
sclerotia 


Floccose. 


Stem plugs . 


22.5 to 43.6 

by 2.87 to 
4.11 M , 14 
days old 


Salmon- 
colored; 
small 


Green, very 
small; 
numerous 


White, 
sometimes 
green near 
sclerotia 


Floccose; 
scant. 



24 Agricultural Experiment Station Research Bulletin l.'± 



Table 2 (Continued). — A morphological comparison of the 

species of Fusarium on soy hean and coin pea. 

F. tracheiphilum. 



Medium 


Macro- 
conidia 


Sporodochia 


Sclerotia 


Color of 
mycelium 


Character 
of mycelium 


Standard 




None 


Flesh- 
colored 


White 


Mostly sub- 
merged or 
appressed 


nutrient 
agar 




String-bean 
agar 


No measure- 
ments 


Salmon- 
colored; 
few 


Mostly 
flesh- 
colored; 
some green 


do 


do 


Oat hard 
glucose 
agar 


22.5 to 36.9 
by 3.8 to 
4.42 ,x 50 
days old 


Flesh- 
colored 


Dark-green 
and flesh- 
colored 


Mostly dark 
purple; 
some lilac 


Cottony to 
matted and 
appressed 


Steamed rice 








Pinks, reds, 
lilacs, 
purples 














Potato plugs 


24.6 to 36.9 
by 3.28 to 
4.42 » 19 
days old 


Salmon- 
colored; 
often on 
sclerotia 


Flesh- 
colored; 
often none 


Pinks, lilacs, 
greens 


Mostly 
appressed 


Stem plugs. 


No measure- 
ments 


Salmon- 
colored; 
small ; 
sometimes 
none 


Green ; verj- 
small;'* 
numerous 


White ;_ 
sometimes 
green, near 
sclerotia 


Appressed; 
good growth. 



No mention is made in Table 2 of pionnotes or odors, as none 
was produced in any of the cultures. Only color-production was 
noted on steamed rice. The macroconidia of both strains show a 
wide variation both in size and in shape, but these differences can 
properly be included in the range of variation. The normal 
macroconidia of the soy bean (fig. 4, A-G) and cowpea strains are 
indistinguishable. The chlamydospores of either strain are ter- 
minal or intercalary in or on vegetative filaments and average 
6 to 10.25 fx. in diameter. The conidiophores are verticillately 
branched when normal. Sporodochia, altho sometimes flesh- 
colored, are normally salmon-colored. They are not always present 
on all media but are formed by each strain either on sclerotia or 
on mycelia as stromatal bases. Green sclerotia are normally 
present in both strains. There appear to be some differences in 
colors produced in substrata, altho not very consistent ones, a 



Fusarium Blight of the Soy Bean 25 

difference in the character of mycelium until advanced ages of 
the cultures and generally-, but not always, an absence of flesh- 
colored sclerotia in the soy bean fungus. These differences, how- 
ever, are not believed to be of sufficient importance to warrant 
regarding the soy bean strain as a distinct species or variety. 

In addition to the media employed in Table 2, potato hard ■ 
agar, cornmeal plugs, and string-bean pods were used, but they 
showed no additional characters of value. 

Perithecia have never been observed on the diseased stems; 
neither have they been obtained in cultures from the surface spores, 
nor from the diseased internal tissues. In fact, the cultural differ- 
ences between the Fusarium sp. on soy bean and Neocosmospora 
spp. are as striking as between Neocosmospova spp. and the 
several species of Fusarium causing wilt studied by Higgins (14) 
and Butler (3). 

INOCULATION EXPERIMENTS 

From the foregoing morphological and cultural studies, it is 
evident that the species of Fusarium on soy bean is not distin- 
guished from F. tracheiphilum by any well-defined differences. 
Since the possibility existed that they might be separated by 
biological differences, reciprocal inoculation studies were under- 
taken to secure additional evidence of their identity. 1 

Plants were therefore grown in pots and flats in the green- 
house and in plots in the field for use in inoculations. The soil 
used in the pots and flats was a fine, compact, sandy loam, except 
in the case of one experiment, and was taken from a field in 
which diseases of cowpeas and soy beans caused by Fusarium spp. 
had never been observed. In certain of these tests, as an added 
precaution, the soil was partially sterilized by the use of a 2 per 
cent solution of formaldehyde. The seed were also sterilized in 
certain experiments by immersion for 15 minutes in commercial 
sulphuric acid. Since iminoculated plants remained free from 
disease when these precautions were not employed, their use was 
discontinued in subsequent tests, unless otherwise stated. 

The pots and flats were of sufficient size to permit the plants 
to grow to maturity. 

In determining the percentage of diseased plants, count was 
made only of those in which it was possible to find discoloration 
and invasion of the xylem tissues. In case of doubt in this micro- 
scopic examination, planted plates were made from the tissues and 
the subsequent growths studied. 

The varieties of soy beans and cowpeas planted for the cross- 
inoculation experiments were known to be subject in the field to 
the species of F.usarium on soy bean and cowpea, respectively. 

1 Wollenweber (31, p. 37) says that a consideration of the biological characters is of 
secondary importance in the determination of species. 



26 Agricultural Experiment Station Research Bulletin H 



EXPERIMENT I —Twenty-five North Carolina Black cow- 
pea and 25 Mammoth Yellow soy bean seedlings, growing in each 
of two flats in the greenhouse, were each inoculated when from 
10 to 15 cm. high with spores from sporodochia and with 
mycelium by introducing the material into incisions in the stems 
at 2 to 1 cm. below the surface of the soil. All of the plants in 
one flat were inoculated with the soy bean strain of Fusarium 
and all of those in the other with the cowpea strain. Checks and 
all inoculated plants except two cowpeas inoculated with the soy 
bean strain and one with the cowpea strain remained healthy. 
The test was repeated, using freshly isolated strains of both 
organisms ; and, since all but one of the plants remained healthy, 
this method of inoculation was discarded. 

EXPERIMENT II.— In this experiment the soil in two flats, 
A and B, in the greenhouse was inoculated with pure cultures of 
Fusarium spp. on cowpea and soy bean, respectively. These cul- 
tures were then incorporated in the upper 4 inches of soil. 

In this and succeeding experiments the organisms had been 
grown on pieces of moistened, sterilized cowpea steins until 
numerous sporodochia had formed. On April 12, 1916, 20 North 
Carolina Black cowpeas and 20 Mammoth Yellow soy beans were 
planted in each flat. A third flat, containing uninoculated soil, 
was planted as a check. 

By June 4 a cowpea plant on Flat B was noted to be diseased. 
Others had been observed to be affected by June 15, when all the 
plants were removed and examined. The results are presented in 
Table 3. 

Table 3. — Results of growing soy beans and cowpeas in artificially 

inoculated soil. 



Flat 


Organism 


Host 


Total 

number 

of plants 


Disea 


sed plants 


No. 


Percentage 


A 


F. tracheiphilum on cowpea. . 


Cowpeas. . . . 
Soy beans. . . 


20 
20 


6 
3 


30 

15 


B 


Fusarium sp. on soy bean. . . 


Cowpeas. . . . 
Soy beans. . . 


20 
20 


10 

7 


50 
35 


C 


None (control) 


Cowpeas. . . . 
Soy beans . . . 


20 
20 











EXPERIMENT III (Series 1).— Since the percentage of 
diseased plants in Experiment II is relatively small, the test was 
repeated, using another strain of each organism and Clay cow- 



Fusarium Blight of the Soy Bean 



27 



peas instead of North Carolina Black variety. The roots of each 
plant in this test were injured during the process of cultivation. 
The period of growth of these plants extended from June 29 to 
September 1, at which date the plants were fully matured. The 
results of this series are recorded in Table 4 (a). 

EXPERIMENT III (Series 2).— The test in series 1 was 
duplicated between September 7 and November 20, with no re- 
sultant increase in the percentage of infections. 

EXPERIMENT III (Series 3).— This test was in duplica- 
tion of the other series in this experiment except that the soil 
consisted of a mixture of six parts of coarse sand, one part of 
fine sandy loam, and one part of stable manure. The results 
obtained between September 7 and November 20 are included in 
Table 4 (b), because they show considerable increase in the per- 
centage of infection even tho the cultures used were transfers from 
cultures nearly 3 months old. 

Table 4 (a) and (b). — Results of growing soy beans and cowpeas 

in artificially inoculated soil, the plants having been 
(a) wounded below the surface of the soil. 



Flat 


Organism 


Host 


Total 
number 
of plants 


Diseased plants 


No. 


Percentage 


D 


F. tracheiphilum on cowpea. . 


Cowpeas. . . . 
Soy beans. . . 


' 20 
20 


3 
3 


15 

15 


E 


Fusarium sp. on soy bean . . . 


Cowpeas 

Soy beans. . . 


20 

20 


6 
5 


30 
25 


F 


None (control) 


Cowpeas. . . . 
Soy beans. . . 


20 

20 

















(b) 












Flat 


Organism 


Host 


Total 
number 
of plants 


Diseased plants 


No. 


Percentage 


G 


F. tracheiphilum on cowpea . . 


Cowpeas. . . 
Soy beans. . . 


20 
20 


16 

12 


80 
60 


H 


Fusarium sp. on soy bean . . . 


Cowpeas. . . 
Soy beans. . . 


20 
20 


13 
12 


65 
60 


J 


None (control) 


Cowpeas. . . . 
Soy beans. . . 


20 
20 

















28 Agricultural Experiment Station Research Bulletin 1 4 

EXPERIMENT IV.— Since it was thought that the strains of 
Fusarium on soy bean had to a degree lost their virulence by 
growth in culture, soy bean stems bearing an abundance of sporo- 
dochia were macerated and mixed with the soil in two flats. Seed 
of the Mammoth Yellow variety were planted on May 25. When 
the experiment was concluded, August 10, only 8 of the 80 soy 
bean plants in these two flats were found to be infected. 

EXPERIMENT V. — This experiment was designed to con- 
firm the results of inoculations in the greenhouse by inoculations 
under partially controlled field conditions. Four small plots 
(Nos. 2G, 27, 28, and 29) on wilt-free soil of the station farm 
were inoculated with the F. tracheiphilum from soy bean; two 
others (Xos. 59 and 60) with this organism from cowpea, and two 
(100 and 101) were left untreated as controls. Thirty cowpeas 
and thirty soy beans were planted in each plot on June 10, and 
the final results noted in Table 5 were obtained on September 4. 





Table 5.- 


—Results of cross-inoculations in 


the -field. 


Plot 
No. 


Organism 


Host 


Total 
number 
of plants 


Diseased plants 


No. 


Percentage 


26 


Fusarium sp. 
on soy bean 


Clay cowpeas 


30 
30 


17 
4 


56.6 


Haberlandt soy beans 


13.3 


27 


do 


Clay cowpeas 

Tokio soy beans 


30 

30 


10 



33.3 
0.0 


28 

28 


do 
do 


Clay cowpeas 

Mammoth yellow soy beans . 


30 
30 


10 
8 


33.3 
26.6 


29 


do 


Clay cowpeas 

Tar Heel Black soy beans. . . 


30 
30 


15 
3 


50.0 
10.0 


59 


Furarium sp. 
on cowpea. 


Clay cowpeas 

Tokio soy beans 


30 
30 


.26 
6 


86.6 
20.0 


60 

60 


do 

do 


Clay cowpeas 

Mammoth Yellow soy beans . 


30 

30 


17 
6 


56.6 
20.0 


100 


None 
(control) . . . 


Clay cowpeas 


30 
30 






0.0 




Mammoth Yellow soy beans. 


0.0 


101 


do 


Clay cowpeas 


30 
30 






0.0 




Mammoth Yellow soy beans . 


0.0 



EXPERIMENT VI.— On May 25, 1916, two 100-foot rows 
of each of the soy bean varieties Tokio, Haberlandt, Mammoth 



Fusarium Blight of the Soy Bean 29 

Yellow, Medium Yellow, and Virginia were planted in a field 
which produced a large percentage of wilt in cowpeas in 1914. 
Two rows of cowpeas were planted in the same plot. By Septem- 
ber 1, when all the plants had fully matured, a small percentage 
of wilted cowpeas had been noted ; but no blighted soy beans were 
found. 

Similar data were obtained from observations on cowpeas and 
soy beans grown in the experimental plot devoted to plant breed- 
ing. In this 4-acre plot, three or four rows of soy beans were 
alternated with three or four row r s of cowpeas thruout the field. 
Some wilt occurred in practically every row of cowpeas in the 
plot, but careful examinations during the season failed to reveal 
a single soy bean blighted with Fusarium sp. among 17 standard 
varieties and 50 other unnamed selections. 

DISCUSSION OF THE RESULTS OF INOCULATION EXPERI MENTS 

In inoculation experiments soy beans and cowpeas, from the 
time of germination until 4 or 5 days after their appearance above 
the surface of inoculated soil, were often killed by an organism 
which invaded the cotyledons and the growing tips. This was 
especially true if nearly pure sand was used instead of soil. It- 
was not definitely proved that Fusarium was the cause of this 
condition, however, and no record of these cases was made in the 
results given above. 

In the results recorded, the cowpeas after 4 to 6 weeks were 
generally invaded well up into the stem and the plants were often 
killed after a period in which they showed, except for sporo- 
dochia, the striking symptoms commonly known to appear in 
connection with this disease in the field. On the other hand, the 
affected soy beans have shown symptoms only on the roots. Some 
of these were found to have typical discoloration in the xylem 
areas but the root systems were never invaded to the extent that 
the plants showed the effects above the ground. A lack of vigor 
was apparent in many soy beans but it w T as uncertain without 
an examination of the roots whether this was due to the action of 
the organism or to more or less unfavorable conditions for plant 
growth. 

That reciprocal inoculations were successful in a number of 
cases can be seen from the results of certain of the above experi- 
ments in which plants of both hosts became infected by both 
strains of Fusarium. Certain other attempts were made, how- 
ever, in which all soy beans remained free from disease. Contrary 
to this, the cowpeas in the same flats always showed at least 
several plants typically diseased, regardless of whether they 



30 Agricultural Experiment Station Research Bullet hi IJf. 

were growing in soil that had been inoculated with the cow T pea or 
with the soy bean strain of Fusarium. 

EXPERIMENTS ON THE RELATION OF VARIOUS SOIL FACTORS TO 
INFECTION OF SOY BEANS BY F. TRACHEIPHILUM 

THE INFLUENCE OF SOIL TYPES 

Since artificially inoculated soy beans have not always 
developed the disease, nor developed it to the same degree of 
severity that cowpeas have under the same conditions, nor as 
severely as naturally infected soy beans in the field, a number of 
experiments were planned to determine the factor or factors 
which seemed to be responsible for the limitations. At the outset 
possibly all of the factors of the air and soil that influence the 
health of plants might be concerned. The effects of certain of 
these have been under consideration in the following experiments 
in which, with the exception of that on Norfolk soils, all of the 
plants were subjected alike to those factors which it was impossi- 
ble to control. In this way evidence was obtained as to the effect 
produced by certain factors by varying one, under control, in 
each experiment. 

The relation of conditions above the ground, such as tem- 
perature, humidity, and light, to the susceptibility of plants to 
parasitic diseases is often an important one, but a study of them 
in connection with the disease at hand has not yet been made 
because a more direct relation probably exists between soil fac- 
tors and infection. In consideration of the soil, attention has 
first been given to the effect of variation in texture which is 
limited by the size of soil particles and by organic and inorganic 
materials which further influence such factors as temperature and 
water holding capacity. The United States Bureau of Soils has 
divided soils into types, classes, and series. 

Soil class — "Soil types, which constitute the units of soil 
classification, may be grouped in different ways. As soils are 
made up of particles of different sizes, they may be grouped 
according to the relative proportions of the particles of different 
sizes which they contain. This grouping is known as soil class 
and is based on texture." (30, p. 16.) 

Soil series — "It has been found that in many parts of the 
United States a given set of soil classes are so evidently related 
thru source of material, method of formation, topographic posi- 
tion and coloration that different types constitute merely a grada- 
tion in the texture of an otherwise uniform material. Soils of 
different classes that are thus related constitute a series. A com- 
plete soil series consists of material similar in many other charac- 



Fusarium Blight of the Soy Bam 31 

teristics but grading- in texture from stone and gravel on the 
one hand, thru sand and loams, to a heavy clay on the other." 
(30, p. 19.) 

In North Carolina, Fusarium tracheiphilicm occurs mostly 
in the Coastal Plains or eastern one-third of the state and in this 
section the Norfolk soils series is the most important one, not 
only because of its percentage of area but also because of its 
agricultural value. These soils are characterized by the light 
gray to grayish-yellow color of the surface soils and by the yel- 
low color and friable structure of the subsoils. They occupy 
nearly level to rolling uplands thruout the Atlantic and Gulf 
Coastal Plains, and have been derived mainly from Piedmont and 
Appalachian material. 

The writer has observed soy bean blight in the field on sand, 
fine sand, sandy loam, and fine sandy loam soils, but not on those 
with a higher percentage of the finer particles such as silt, silt 
loam, clay loam, or claj^. 1 Inoculations in the greenhouse thru 
mixed soils to which a large amount of coarse sand had been 
added also resulted in a higher percentage of infection. Wollen- 
weber (31, p. 46) concluded, from observations made during his 
inoculation experiments, that light sandy soils 2 favored the de- 
velopment of Fusarium spp. inhabiting the soil and causing wilt 
diseases. 

An experiment was conducted in which soy beans were grown 
in eleven types of soil of the Norfolk series which were collected 
with considerable care from typical localities in the Coastal 
Plains with the assistance of Mr. C. C. Logan of the North 
Carolina Station who has had considerable experience in making 
soil surveys. That there are no well-defined limits to individual 
types, and that different survey parties often disagree in classifi- 
cation and limits of areas, was kept constantly in mind. Conse- 
quently soil maps were used only to assist in the general location 
of several examples of a type from which an average could be 
selected. Furthermore, as nearly as it was possible, soils were 
selected which contained a normal amount of humus for the type 
and to which fertilizers had not been added since the previous 
crop had been harvested but to which they had been added in 
the form of complete commercial fertilizers for the benefit of that 
crop. So far as known neither soy beans nor cowpeas had ever 
been grown on these soils. 

Each type was obtained in quantities of GOO pounds. Two 
hundred pounds of the first six inches (surface), 200 of the second 

1 The soil referred to previously by the writer (6, p. 424) as a clay was instead Cecil 
sandy loam. 

-By this term it is supposed that he referred to soils with a larger percentage of 
coarse than of fine particles. 



32 Agricultural Experiment Station Research Bulletin 14 

six (subsurface), and 200 of the third six (subsoil) were placed 
in separate sacks, transported to the station at West Raleigh, and 
replaced at their original depths, in wooden frames sunk to the 
level of the surrounding soil. These types were arranged in a 
sequence according to the increase in the percentage of fine par- 
ticles. The types used were as follows and were arranged in the 
order given : Coarse sand. sand, fine sand, very fine sand, coarse 
sandy loam, sandy loam, fine sandy loam, very fine sandy loam. 
loam, silt loam and clay (30). 1 When arranged in this way, 
variation in the sequence from type to type was evident. They 
were each artificially infected with F. tracheiphilum from soy 
bean and the nematode (Heterodera radicicola). A liberal num- 
ber of nematode galls from the roots of plants not susceptible to 
Fusarium and cultures of the fungus on cut stems were incor- 
porated into the upper six inches of soil. Soil acidity tests indi- 
cated that the different lots ranged from approximately neutral to 
slightly acid. 

At best it was hoped to obtain, quite approximately, a series 
each part of which should vary from the others in its mechanical 
analysis but as little as possible in all other respects, and from any 
variations that might appear in the number and severity of result- 
ing infection to get some indication of the cause for the same. 
If the results should warrant it, a careful physical and chemical 
analysis could be made from samples of each type that had been 
set aside for this purpose before the seed were planted. 

Soy beans and cowpeas were planted on July 3, 1917, and the 
cowpeas were removed after the disease occurred on several of 
them in each flat. The soy beans were harvested on September 26, 
at which time the plants were mature. The results are presented 
in Table 6. 



1 For the mechanical analysis of these types see 30, pp. 46-54, and soil surveys of 
various regions containing these types. 



Fusarium Blight of the Soy Bern 



33 



Table C. — Influence of soil types on percentage of infection by 

Fusarium spp. in the presence of the nematode 
(Heterodera radicicola) . 



Type 


Total 

number of 

plants 


Number 

with 

nematodes 


Per cent 

with 

nematodes 


Number 

with 
Fusarium 


Norfolk coarse sand 


25 


4 


16 







Norfolk sand 


30 


8 


26.6 







Norfolk fine sand 


34 


8 


23.5 


o 






Norfolk very fine sand 


34 


6 


17.6 





Norfolk coarse sandy loam. . . 


33 


5 


15.1 





Norfolk sandy loam 


33 


8 


24.2 


o 






Norfolk fine sandy loam 


31 


4 


12.9 





Norfolk very fine sandy loam . 


25 


7 


28.0 





Norfolk loam 


15 


12 


80.0 


o 






Norfolk silk loam 


17 


1 


5.8 


o 






Norfolk clay 


30 





0.0 






None of the plants were infected by the fungus and conse- 
quently the original purpose, for which the experiment was 
planned, failed. The results, however, are included since they 
furnish some evidence that previous failures of a similar nature 
were not due primarily to the use of soils of unsuitable type, 
water holding capacity, or humus content. The percentage of 
infection of cowpeas, however, seems to be increased when grow- 
ing in inoculated soils containing an excessive amount of humus. 

THE INFLUENCE OF ACIDITY AND ALKALINITY 

No definite experiments have yet been undertaken to deter- 
mine the influence of soil acidity on the development of the dis- 
ease, but field observations indicate that it is not a factor of pri- 
mary importance. They have shown that the cowpea wilt is 
destructive on soils varying considerably along the plus and minus 
scale of acidity. 

A similar conclusion can be drawn from the following cul- 
tural studies. Two strains of F. tracheiphilum, one from cowpea 
and one from soy bean, were grown on a culture medium whose 
reaction was varied from -j-40 to — 10 (Fuller's scale) by the 
addition of standard solutions of NaOH and HC1 to a standard 



34 



Agricultural Experiment Station Research Bulletin 14 



nutrient agar, the original acidity of which was -\-8. Phenol- 
phthalein was used as an indicator. The results presented in 
Table 7 do not include the measurements of colonies on cultures 
the acidities of which were above +25, for the reason that the 
medium was liquefied by so large an amount of acid. Fairly good 
growth was obtained thereon, however, in 4 or 5 days. 

Table 7. — Growth of F. tracheiphilum at varying degrees of 

acidity. 



Age of 

colony 

in hours 


Diameter of colonies in mm. at various degrees of acidity' 2 


+25 


+20 


+ 15 


+10 


+5 





—5 


—10 


—15 


—20 


—25 


—30 


—35 


—40 


24 


9 


10 


9 


9 


9 


9 


10 


10 


10 


8 


8 


8 












42 


26 


25 


99 


22 


24 


21 


21 


20 


18 


19 


18 


18 














68 ... . 


43 


43 


41 


42 


37 


33 


32 


30 


29 


27 


24 


24 


22 


22 


92 


55 


55 






48 


43 


40 


37 1 


34 


36 


36 


36 


34 


34 










115 


66 


64 


66 


66 








441 


42 








42 


42 


















140 ... . 


77 


78 


74 


72 


63 T 


60 


60 


53 


50 


53 


52 


53 


48 


49 


165. . .. 


83 


83 


80 


80 


69 


67 1 


66 


60 


67 


63 


63 


62 


62 


62 



The strain from soy bean 



Age of 

colony 

in hours 


Diameter of colonies in mm. at various degrees of acidity 2 


+25 


+20 


+15 


+10 

7.5 


+ 5 
9.5 



9 


—5 
9 


—10 

7 


—15 


—20 


—25 


—30 


—35 


—40 


24 


12 


9 


7 


6 


8 


8 


8 












42 ... . 


23 


24 


18 


20 


23 


22 


21 


19 


18 


17 


17 


18 










68 ... . 


40 


41 


38 


39 


35 


34 


33 


32 


31 


28 


28 


28 


25 


25 


92 


53 


53 






47 


46 


44 


39 


38 


39 


39 


40 


36 


35 










115 


60 


62 


62 


64 








47 


47 








40 


39 


















140 


69 


73 


70 


72 


66 


64 


10 


55 


55 


55 


51 


57 


50 


47 


165 


83 


83 


79 


80 


76 


75 


68 


68 


63 


67 


68 


67 


60 


57 



The strain from cowpea 



■"Contaminations. 

2 The figures are approximate to within 2 or 3 mm., and are an average of the meas- 
urements from ten plates. 



Fusarium Blight of the Soy Bean 



35 



From an examination of the table as a whole it is evident in 
the case of both strains of the organism that there was better 
growth in the presence of various amounts of acid than in the 
presence of alkali, but that even on a strongly alkaline sub- 
stratum the colonies required only 2 or 3 days longer in which 
to extend themselves over the entire surface of the medium in a 
petri dish. 

Edgerton (7, p. 12) reports field tests with F. lycopersici in 
which tomato wilt was only temporarily checked by the applica- 
tion of lime. He says, "The heavy application of lime (10 tons 
per acre) decreased the wilt and the plants produced a larger 
yield of tomatoes. * * * As the season advanced, however, 
most of the plants in the treated plot also died with the disease," 



THE INFLUENCE OF THE NEMATODE (HETERODERA RADICICOLA) 

As noted in the above experiment with the eleven types of 
the Norfolk series of soils, nematodes had been introduced with the 
Fusarium cultures into each flat, This experiment differed from 
others in which nematodes were present in that the conditions 
were those of the field under slight modification. The plants 
were grown to maturity and only a few nematodes were present 
on the plants indicated as affected with nematodes. Twenty-three 
per cent of the total number developed galls, however, but none 
showed symptoms of the blight, altho the cultures were known to 
be virulent for the reason already stated. 

Table 8. — Influence of nematodes on the percentage of infection 
by F. tracheiphilum. 



Organism 


Total 
number 
plants 


No. with 

nematode 

galls 


No. with 

Fusarium 

sp. 


F. tracheiphilum from cowpea and nematodes . . 


10 


10 


2 


F. tracheiphilum from cowpea without 


10 












F. tracheiphilum from soy bean and nematodes . 


10 


10 


3 


F. tracheiphilum from soy bean without 


10 





2 








10 


10 











20 













36 Agricultural Experiment Station Research Bulletin 14 

A previous test had been made with soy beans, between 
September 26 and December 1, 1916, in an attempt to determine 
whether the presence of nematodes increases the number of in- 
fections. The nematodes were introduced into the soil of large 
buried pots in root galls from living soy beans free from infection 
by Fusarium spp. The results are presented in Table 8. 

At Lincoln, on December 4, 1917, six stone jars of five gallons 
capacity were rilled with nematode infested soil from a greenhouse 
bench in which badly nematode-infected tomatoes were growing. 
Four other jars were filled with nematode-free potting soil. Cul- 
tures of Fusarium growing on pieces of sweet clover (Melilotus 
alba) stems, from two 1 liter flasks, were incorporated into the 
soil of each jar. Three Clay cowpeas and three Mammoth Yellow 
soy beans were grown to maturity in each jar in a greenhouse 
kept at approximately 28° C. during the day and 22° C. at night. 
On February 16, when the plants had nearly matured seed pods, 
they were removed and examined. Table 9 shows the number of 
plants affected with nematodes and with Fusarium. 



-Influence of nematodes on infection by 
F. tracheiphilum. 



Jar 
No. 


Organisms 


Total number 
of plants 


Per cent affected 
with nematodes 


Per cent affected 

with Fusarium 

i 


Soy bean 


Cowpea 


Soy bean 


Cowpea 


Soy bean 


Cowpea 


1 


Fusarium and 
nematodes. . . 


3 


3 


100 


100 





100 


2 


do 


3 


3 


100 


100 





100 


3 


do 


3 


3 


100 


100 





100 


4 


do 


3 


3 


100 


100 





100 


5 


do 


3 


3 


100 


100 





100 


6 


do 


3 


3 


100 


100 





100 


7 


Fusarium 


3 


3 











33§ 


8 


do 


3 


3 











66f 


9 


do 


3 


3 











66f 


10 


do 


3 


3 











33 i 



Fusarium Blight of the Soy Becm 37 

It is to be noted that all of the plants in the last test wore 
infected with nematodes but that the cowpeas were more severely 
affected, the galls being somewhat larger and more numerous. 
The cowpeas generally showed symptoms of the fungus whether 
the eelworms were present or not. The soy beans remained free 
from the fungus in spite of nematode injuries. The galls on 
the soy beans did not reach a diameter of more than 1 to 2 mm. 
whereas in the fields where the blight developed they were 
commonly 8 to 10 mm. in diameter. The presence of the galls 
even tho small, and the absence of the fungus on the roots of 
plants in soil infected with both organisms in this and the two 
other tests mentioned, is evidence that the presence of nematodes 
under conditions which favor the development of the fungus on 
cowpeas does not supply the conditions that obtain in the field, 
which allow the development of this fungus on soy beans. 

THE INFLUENCE OF SOIL TEMPERATURE 

Recent reports of various investigators point out the relation 
of temperature to diseases caused by soil inhabiting fungi espe- 
cially species of Fusarium,. Jones (15) emphasizes the impor- 
tance of this factor by summarizing the results of these investiga- 
tions and correlating them with his own field observations. In 
main the results with Fusarium spp. show a minimum tempera- 
ture for infection around 15° to 17° C. and a rather broad 
optimum of about 25° to 30° C. As far as the writer is aware, no 
data on maximum temperatures have been reported. 

Before attempting to determine the influence of certain tem- 
peratures on sov bean blight, the organism was tested in culture 
at constant temperatures of 5°, 8°, 12°, 16°, 20°, 28°, and 33° C. 
After 10 days at 5° there was practically no growth, at 8° the 
colonies averaged 1 or 2 mm. in diameter, at 12° they were about 
5-7 mm., at 16° about 18-20 mm., and with a rise in temperature 
to 28° a corresponding increase in size of colonies. At 33° the 
growth was someAvhat less than at 28°. Cultures of the other 
wilt producing species of Fusarium reported by others correspond 
rather closely in their growth at these temperatures. 

The optimum condition for infection in the case of soy bean 
blight may, however, be entirely different from that which is 
favorable to either parasite or host. Experiments are now in 
progress in which soy beans are growing in inoculated soil main- 
tained at various constant temperatures. Nothing of significance, 
however, can at present be reported as to the relation of this 
factor, except that the amount of disease has not been increased 
at 14, 16, 17, or 24 degrees Centigrade. 



38 Agricultural Experiment Station Research Bulletin IJf 

THE INFLUENCE OF OTHER ORGANISMS 

It is very possible that a larger number of infections and a 
more extensive development of the fungus within the host occur 
in the field than under the conditions of controlled inoculations 
because of the presence in the former of associated parasitic 
organisms and the injuries caused by them, or because of other 
injuries of the roots caused by insects, mechanical tools, or im- 
proper culture. This may oftentimes be of especial importance 
in connection with Fusarium spp., which are not as strict para- 
sites as some and therefore enter more readily thru wounds. Two 
such organisms of the soil, namely, Rhizoctonia and Sclerotium 
rolfsii, were noticed affecting soy beans in fields where the 
Fusarium blight was abundant. The soy bean is more resistant 
to Rhizoctonia than most garden and field crops but lesions were 
noted on seedlings, young plants, and the small roots of older 
plants. Sclerotium rolfsii, however, is very destructive to soy 
beans whenever present and kills plants at all stages of their 
growth. 

Soy beans are now growing in soil inoculated with Fusarium 
tracheiphilum and Rhizoctonia, and in another soil inoculated 
with Fusarium tracheiphilum and Sclerotium rolfsii, and it is be- 
lieved by the writer that either these or other organisms will be 
found to play an important part in the development of this dis- 
ease. It seems probable from preliminary tests that Fusarium 
tracheiphilum is unable to penetrate soy bean roots to the xylem 
elements unaided but that, once it gains entrance thereto, it 
develops rapidly in them in a somewhat saprophytic manner, 
obscures the primary injury, and finally affects the host as 
previous^ described. 

FIELD EXPERIMENTS TO DETERMINE THE SUSCEPTIBILITY OF 

VARIETIES 

Sixty per cent of the Mammoth Yellow soy beans in the field 
at Ked Springs, N. C, were blighted in 1915. The main part 
of this field was planted to the same variety on May 23, 1916; 
but in another part reserved for the purpose, one 54-meter row 
each of Haberlandt, Mammoth Yellow, Pekin, Black Eyebrow, 
Medium Yellow Virginia, and Tar Heel Black soy beans and a 
row of Clay cowpeas were planted on June 8. On August 10 
the main field and all of the varieties in the test, including the 
cowpeas, showed considerable blight or wilt, except the Black 
Eyebrow and the Virginia varieties of soy beans. On August 26 
the latter of these varieties was apparently free from disease, but 
the plants had declined with age to such an extent that the exact 



Fusarium Blight of the Soy Bean 39 

determination was. doubtful. The fact that these varieties were 
planted so late that hot, dry weather prevailed during a large 
part of their early growth explains why they were so rapidly 
forced to maturity. The Black Eyebrow variety remained free 
from disease thruout the season. An examination of plants in all 
parts of the field showed that the disease was abundantly and 
uniformly distributed. 

Since the Black Eyebrow variety, which was planted late in 
1916, i. e. June 8, remained free from the disease, it was planted 
again at intervals in 1917 in order to observe the effect of seasonal 
planting on the development of the disease. The first planting 
was made on April 26, another on May 31, and a third on June 
21. The ground was hardly suitable for planting between these 
dates. Plants from the second and third planting were much 
dwarfed because of unfavorable weather, severe nematode infec- 
tion, and a lack of cultivation, and for this reason no certain 
results as to the amount of infection in the different plantings 
were obtained. The most important determination possible from 
these observations is that some other variety more suitable to 
late planting should be used in future tests for this purpose. 
Since the Black Eyebrow variety remained free from the disease 
in 1916, it is important to note that a few diseased plants of this 
variety were found in the general variety test rows referred to 
below where the seed were planted earlier. However, the variety 
seems to show some evidence of resistance. 

A larger number of varieties were tested in this field in 1917. 
Three rows each of the following varieties were planted on April 
26: Brown, Black Eyebrow, Virginia, Mammoth Yellow, Early 
Dwarf Green, Wilson Black, Barchet, Jet, Austin, Arlington, 
Guelph, Chiquita, Auburn, Manchu, Tokio, Peking, Tar Heel 
Black, Haberlandt. and Medium Yellow. Every tenth row was 
planted to Clay cowpeas, and one row of the One Hundred Day 
Speckle velvet bean (Mucuna utilis) was planted around two sides 
of the field. By July 20 the disease was abundant in all of the 
varieties of soy beans except the Black Eyebrow discussed above. 
The cowpeas Avere so badly diseased that all died before blooming. 
The velvet beans were entirely free from nematodes or Fusarium. 

The Brown variety, altho as badly infected by the nematode 
and Fusarium as any of the other" varieties, deserves special men- 
tion because of its tolerance to these parasites. In spite of the 
presence of a large number of nematode galls, varying in diameter 
from 1 to 15 mm., and the presence of Fusarium, thruout the xylem 
area of the roots and for some distance up the stem, there was 
absolutely no wilting, no chlorosis, nor any external evidence of 
any infection whatsoever. The plants were from four and one- 



40 Agricultural Experiment Station Research Bulletin 14 

half to five and one-half feet in height, they stood six inches to a 
foot above any other variety and more than that above the Mam- 
moth Yellow ; they remained green and healthy in appearance 
thruout the season and produced a good crop of beans which 
were about mature on September 8, when the field was pastured 
to hogs. Perhaps the size of these plants was somewhat reduced 
by the action of the two organisms. Unfortunately there were 
no check plants with which these could be compared since the 
entire field was infected. Affected plants of this variety, how- 
ever, yielded us well as the average healthy Mammoth Yellow 
plants in nearby fields. 

The Brown S03 7 bean is identical with the Mammoth Yellow 
in habit-type and is very similar to it in other respects. The color 
of the seed is the only apparent difference. This variety has been 
grown but very little in North Carolina, but tests have shown that 
it is as desirable in every respect, if not more so, than the present 
favorite variety, the Mammoth Yellow, which suffers greatly 
from Fusarium blight. Mr. Walter White at Edenton, N. C., says 
that he prefers the Brown to the Mammoth Yellow because it 
produces more forage and more seed and can be grown wherever 
conditions are favorable to the Mammoth Yellow. 

The Haberlandt variety, which is also suitable to conditions 
in North Carolina, develops well in spite of rather severe 
Fusarium and nematode infection. 

The Brown and Haberlandt varieties are preferable to the 
Black Eyebrow for planting in infected soil, especially if nema- 
todes are present, even tho the latter should remain free from 
Fusarium infection. 



Fusarium Blight of the Soy Bean 41 

SUMMARY 

I. A disease of the soy bean has been studied during the past 
three years. The tirst report of this disease appeared in a publi- 
cation by the writer in li>17. 

II. The disease is characterized by a chlorosis and shedding 
of the leaves or leaflets, followed by the death of the plants, and 
is herein called "blight." 

III. Soy bean blight has bsen observed in several localities 
within North Carolina on soils infested with cowpea wilt. What 
is probably the same disease has been recently observed by others 
in Alabama and possibly in Wisconsin. 

IV. A species of Fusarium belonging to the section Elegans 
is the causal organism. 

V. Cultural and morphological studies which are regarded 
as of primary importance in distinguishing species of Fusarium 
show that the strain of Fusarium on soy bean is identical with the 
organism producing the wilt of cowpeas. 

VI. Eeciprocal inoculation experiments with the strains 
from soy beans and cowpeas show that cross-inoculations can be 
made. These experiments were conducted in the greenhouse and 
under field conditions. Pure cultures of the two strains were used 
in certain of the experiments and inoculum from the natural 
host in others. 

VII. Blight of soy beans is therefore due to Fusarium 
tracheiphilum. 

VIII. Physical structure and acidity of the soil under 
natural conditions are not the limiting factors in infection, but 
acidity under certain conditions may have some influence; 

IX. Infection occurs thru the roots, but nematodes appear 
not to increase the percentage of blight materially. Other organ- 
isms such as Rhisoctonia and Sclerotium rolfsii and other root 
injuries arc believed to materially increase the percentage of dis- 
eased plants in the field. 

X. The Black Eyebrow variety of soy beans shows some 
evidence of resistance. The Brown variety, while not resistant, 
is tolerant and seems to develop remarkably in spite of numerous 
fungous filaments and nematodes within the roots. Fifteen other 
varieties tested are severely affected. Velvet beans are not sub- 
ject to infection. 



42 Agricultural Experiment Stat ion Research Bulletin 14 



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Butler, E. J. 
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1916. Chlorosis and crinkling of the soy bean. Rpt. Conn. Exp. 
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Cromwell, Richard O. 

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Edgerton, C. W. 

1918. A study of wilt resistance in the seed bed. Phytopathology 
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Engler, Adolf. 
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Fusarium Blight of the Sot/ Bean 43 

(17) Manns, T. F., and Taubenhaus, J. J. 

1913. Streak: A bacterial disease of the sweet pea and clovers. 
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(18) Massalongo, C. 

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(19) Orton, W. A. 

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(20) Piper, C. V. 

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(21) and Morse, W. J. 

1910. The soy bean; history, varieties, and field studies. Bui. 
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(22) Scofield, C. S. 

1912. The nematode gallworm on potatoes and other crop plants 
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(23) Sherbakoff, C. D. 

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(24) Smith, Erwin F. 

1911. Bacteria in Relation to Plant Diseases, v. 2, Washington, 
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(25) Sydow, Hans; Sydow, Paul; and Butler, E. J. 

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(26) Taubert, P. H. W. 

1894. Leguminosae. In Engler, Adolf, and Prantl, K. A. E. Die 
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( 27 ) Thiimen, Felix von. 

1877-80. Symbolae ad floram mycologicam austriacam. Oesterr. 
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(28) Tisdale, W. H. 

1917. Flax-wilt: A study of the nature and inheritance of wilt 
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(29) U. S. Bur. Census. 

1913. Statistics for North Carolina. In U. S. Bur. Census, 13th 
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(30) U. S. Bur. Soils. 

1906. Soil Survey Field Book. 

(31) Wollenweber, H. W. 

1913. Studies on the Fusarium problem. Phytopathology 3:24-50. 
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(32) 

1914. Identification of species of Fusarium occurring on sweet 
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pi. 12-16 (1 colored). 

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